The overall goal of this proposal is to determine the effectiveness of fibrocytes as novel antigen delivery systems for FHV vaccines. Recent studies have identified a novel population of blood-borne cells, termed fibrocytes, that have a distinct cell surface phenotype (CD34+/collagen/CD13/CD45'), and express each of the known surface components that are required for antigen presentation, including class I and class II MHC molecules (HLA-DP, -DQ, and -DR), the co-stimulatory molecules CD80 and CD86, and the adhesion molecules CD 1la, CD54, and CD58. Human fibrocytes induce antigen presenting cell (APC)-dependent T-cell proliferation and this proliferative activity is as high as that induced by purified dendritic cells (DC). In their present form, fibrocytes are significantly easier to isolate and culture than are dendritic cells. Importantly, mouse fibrocytes pulsed in vitro with the HIV-proteins p24 or gp120 and delivered to a site of cutaneous injury migrate to proximal lymph nodes and specifically prime naive T cells. The proposed studies will optimize growth and culture conditions for ex vivo macaque fibrocyte growth, antigen display, and induction of T-ceU responses measured both in vitro and in vivo. Based upon the investigators' previous vaccine experience in the SIV system, they propose to study fibrocytes as a direct vaccination strategy. The application has five major research goals: (1) to characterize macaque fibrocytes in vitro with respect to longevity, their ability to replicate, cryopreservation, and infectivity with lentiviruses in vitro and in vivo; (2) to measure the expression of SIV and HIV-1 viral proteins in uninfected macaque fibrocytes following DNA infection; (3) to determine whether fibrocytes are antigen presenting cells following DNA immunization in vivo; (4) to determine qualitative and quantitative differences in immune responses in vivo using autologous macaque fibrocytes presenting antigen-pulsed versus DNA-transfected SIV proteins; and (5) to determine the effectiveness of fibrocytes charged with pseudovirions or transfected with DNA encoding viral antigens to generate host immunity by challenging immunized macaques with pathogenic SIV. The hypothesis to be tested is that optimal antigen presentation in vivo may be approached by direct testing of known antigen presenting cells to facilitate the development of immune responses that are more similar to those obtained during lentiviral infection. It is expected that positive data from these studies will provide the basis for vaccine experiments involving autologous fibrocytes for HIV vaccines, as well as information to assist in the design of optimal and novel vaccines that are effective in preventing infection and disease.